1.1 Field of the Invention
The present invention relates generally to the fields of insect control. Certain embodiments concern methods and compositions comprising nucleic acid segments which encode Bacillus thuringiensis-derived .delta.-endotoxins. Disclosed are methods of altering Cry1 crystal proteins by mutagenesis of the loop regions between the .alpha.-helices of the protein's domain 1 or of the loop region between .alpha.-helix 7 of domain 1 and .beta.-strand 1 of domain 2 to give rise to modified Cry1 proteins (Cry1*) which have improved activity against Lepidopteran insects. Various methods for making and using these recombinantly-engineered proteins and nucleic acid segments, including development of transgenic plant cells and recombinant host cells are also disclosed.